build(gulp): turn off dartfmt logs by default

Closes #2105

gulpfile.js

@@ -34,7 +34,19 @@ var util = require('./tools/build/util');
 var bundler = require('./tools/build/bundle');
 var replace = require('gulp-replace');
 var insert = require('gulp-insert');
+var shouldLog = require('./tools/build/logging');
 
+// Make it easy to quiet down portions of the build.
+// --logs=all -> log everything (This is the default)
+// --logs=quiet -> log nothing
+// --logs=<comma-separated-list> -> log listed items.
+//
+// Not all commands support optional logging, feel free
+// to add support by adding a new key to this list,
+// and toggling output from the command based on it.
+var logs = {
+  dartfmt: shouldLog('dartfmt')
+};
 
 // dynamic require in build.tools so we can bootstrap TypeScript compilation
 function throwToolsBuildMissingError() {
@@ -194,7 +206,7 @@ gulp.task('build/pubbuild.dart', pubbuild(gulp, gulpPlugins, {
 
 gulp.task('build/format.dart', function() {
   return util.processToPromise(spawn(DART_SDK.DARTFMT, ['-w', CONFIG.dest.dart], {
-    stdio: 'inherit'
+    stdio: logs.dartfmt ? 'inherit' : ['ignore', 'ignore', 'inherit']
   }));
 });
 

tools/build/logging.js

@@ -0,0 +1,43 @@
+var kLogsArgument = /^--logs\s*=\s*(.+?)$/;
+var kTrimLeft = /^\s+/;
+var kTrimRight = /\s+$/;
+var kCamelCase = /[-_\s]+(.)?/g;
+var logs = findArgvLogs();
+
+function findArgvLogs() {
+  for (var i = 0; i < process.argv.length; ++i) {
+    var match = process.argv[i].match(kLogsArgument);
+    if (match) {
+      return logsToObject(match[1]);
+    }
+  }
+  return null;
+}
+
+function logsToObject(logstr) {
+  return logstr.
+    split(',').
+    reduce(function(obj, key) {
+      key = camelize(key);
+      if (key.length > 0) obj[key] = true;
+      return obj;
+    }, Object.create(null));
+  return logs;
+}
+
+function camelize(str) {
+  return str.
+    replace(kTrimLeft, '').
+    replace(kTrimRight, '').
+    replace(kCamelCase, function(match, c) {
+      return c ? c.toUpperCase() : "";
+    });
+}
+
+function shouldLog(str) {
+  if (!logs || logs.quiet) return false;
+  if (logs.all) return true;
+  return !!logs[camelize(str)];
+}
+
+module.exports = shouldLog;